This invention relates to hand-held light sources, and more particularly to flashlights having means to turn themselves off after a predetermined interval, particularly when used by children. It further relates to the incorporation in general purpose household flashlights of bypass and "child-proofing" mechanisms such that if such flashlights are played with by children their batteries will not be completely drained, but will retain power for service in emergencies. Furthermore, the bypass mechanism can be used to ensure that the flashlight will not turn itself off during an emergency or other situation in which uninterrupted service is desired.
Hand-held light sources have been used in one form or another for millennia. Ancient legend recounts Diogenes' fruitless search for an honest man as having been conducted with the unaviling aid of a hand-lantern. Prehistoric light sources were doubtless torches, but the invention of the oil lamp made possible the hand-lantern, its wick sheltered in a wind-proof housing. At a later stage, candles supplanted the oil lamp, only themselves to yield to kerosene lamps in the late 19th century. Carbide lamps, in turn, supplanted those in such applications as mining, until modern times, when the perfection of durable dry cells made what the English call the electric torch, and what is known in America as the flashlight, a practical alternative.
Until the invention of the flashlight, all hand-lanterns employed a flame and a reservoir of flammable material, whether liquid or solid. Such lanterns were capable of igniting a conflagration in the home, the barn or the workplace, and were therefore reserved exclusively for use by adults, since no child could be trusted to handle one safely. However, the advent of the flashlight eliminated that danger, and while flashlights retain their essential role of safe and convenient portable light sources, they have become widely available to children as toys.
No parent will permit a child to play with matches or candles, but most will indulgently permit their children to use their bedsheets as a tent, and to pretend to "camp out" on their beds, reading their favorite book by the light of a flashlight. Of course, the children are soon fast asleep, but when parents tiptoe in to tuck them in for the night, the flashlight buried in the bedclothes is often forgotten, and by morning its batteries are fully discharged.
Similarly, when children are sent off to summer camp with the obligatory flashlight, its batteries are typically discharged during the first evening hike or campfire entertainment. All children are adept at switching on a flashlight, but none seems capable of switching one off.
Since most modern batteries are leakproof and will not ruin a flashlight by leaking when fully discharged, it might be imagined that the cost of replacing batteries is the only consequence of such unintended discharge. However, the more serious problem is the fact that in a household with children even flashlights reserved for emergency use are subject to the same fate. A flashlight is as irresistible to a child as the proverbial flame is to a moth. Every flashlight within reach is used as a toy, and no shelf is high enough, nor any hiding place secret enough to keep a flashlight from a child's reach. When, in an emergency, a parent tries to switch one on, its failure to respond with even a dim glow testifies to the child's diligence in searching out the irresistible plaything.
As noted earlier, the central problem is to get the flashlight swithched off. A child's attention span is short, so the play centered on the flashlight is soon replaced by another game or interest, while the flashlight is abandoned to discharge its batteries unnoticed.
Ordinary flashlights have addressed some of these concerns in a limited manner by often including a button that can be pressed in lieu of turning on the main power switch in order to turn the light on momentarily. Primarily, this added element was intended to permit on-off or Morse-code signaling or flashing--an early feature that gave rise to the appellation "flashlight"--rather than as a means to conserve batteries. Other, small, flashlights have been sold which included switches whose contacts are closed when the barrel of the flashlight is squeezed. None of such mechanisms, of course, will by themselves keep the flashlight lit after they are let go of, and hence their utility for the purposes discussed herein is limited.
Various methods of providing a flashlight with a delayed means of deactivation are also known in the art. These address more directly the concerns noted above, although each such prior art device has distinct disadvantages. Mallory, in U.S. Pat. No. 3,535,282, disclosed a flashlight in which means, such as a spring and bellows arrangement utilizing a controlled air leak to control decompression of the spring, were employed to open the power switch in a flashlight after a predetermined interval. Auer, in U.S. Pat. No. 4,875,147 disclosed a flashlight that employed a suction cup as a delayed action element to control the release of a power switch. An electronic means for obtaining a delayed action is employed in toy flashlights sold by Playskool, Inc. and by Fisher-Price Toys. The Playskool flashlight uses a resistor-capacitor timing circuit to apply a bias to a solid-state switching element in order to shut off the flashlight after about a 30-second interval following a child's release of a handle containing a spring-loaded on-off switch. The Fisher-Price flashlight uses an electronic timing circuit simply to turn off the flashlight after about 20 minutes.
It is observed that the above-mentioned delayed-action prior art devices provide no means for overriding the self-extinguishing mechanism in order to enable unattended use for extended periods when so desired. In the ordinary household use of a flashlight it is sometimes necessary to be able to have the light remain on for an extended period without having to hold or keep reactivating the flashlight. The absence of such a capability prevents such prior art devices from fully meeting the requirements of a general-purpose household flashlight.
In addition, the devices disclosed by Auer and Mallory operate by turning off the main power switch itself, which tends to limit the available delayed action devices to bulky and relatively complicated mechanical structures. Furthermore, the device sold by Playskool employs a solid-state switch which entails a drop of approximately one-half volt across a semiconductor junction, noticeably reducing the brightness of the flashlight.